Chapter 1 Basic Radio Theory Flashcards
Define a hertz
1 complete cycle (1 Hz = 1 wave per second)
Define the wavelength
The distance between a peak and the next peak
Define phase
The difference in angle between to waves
What is the frequency range of very low frequency (VLF)?
3khz - 30khz
What is frequency of low frequency (LF)?
30khz - 300khz
What is the frequency range if medium frequency (MF)?
300khz - 3mhz
What is the frequency range of high frequency (HF)?
3mhz - 30mhz
What is the frequency range of very high frequency (VHF)?
30mhz - 300mhz
What is the frequency range of ultra high frequency (UHF)?
300mhz - 3ghz
What is the frequency range of super high frequency (SHF)?
3ghz - 30ghz
What is the frequency range of extremely high frequency (EHF)?
30 ghz - 300ghz
What is the speed of light?
300,000,000 m/s (3*10^6)
300,000 km/s
162,000 nm/s
What is the formula relation frequency, speed of light and wavelength?
F = c/lambda
F = frequency (Hz) c = speed of light Lambda = wavelength (metres)
What is modulation?
The process of adding intelligence or information to a carrier wave
What are the four types of modulation?
Pulse modulation/keying, amplitude, frequency and phase
What does phase modulation require?
A complex demodulator
Where is phase modulation used?
In GPS receivers
What does modulation create?
Upper and lower frequency known as side bands (e.g. a modulation of 2Hz creates a bandwidth of 4Hz)
Why are single side bands used for HF comms?
Reduces the requirement for the power needed to transmit the signal
What are the 6 types of antennas?
Dipole, loop, parabolic, phases array, slotted planar array and helical
What is the orientation of the magnetic (H) field and the electric (E) field on a vertical antenna?
Magnetic = horizontal Electric = vertical
What is the most basic antenna?
A dipole antenna
What does a dipole antenna consist of?
Two unipole antennas
How much does each pole contribute to the total wavelength?
One quarter (so dipole = half of the wavelength)
What are the three categories of radio waves?
Ground, sky and space waves
Where is the weakest reception on a dipole antenna?
Directly above it
Define diffraction
The ability of a radio wave to follow the curvature of the earth
How does diffraction vary with frequency?
The lower the frequency the greater the diffraction
Define attenuation
How much a radio wave deteriorates (high attenuation is bad)
What is the main propagation method of HF radio waves?
Sky waves (still some ground waves)
What is the relationship between frequency and refraction?
The lower the frequency the greater the refraction
How does a radio wave react when it meets the ionosphere?
It refracts (IT DOES NOT REFLECT)
Why don’t VHF waves diffract?
Too low frequency
What is the attenuation like of VHF waves?
Very high attenuation
What are the three alternative names for VHF waves?
Line of sight waves, space waves and direct waves
How does attenuation vary with frequency?
The lower the frequency the lower attenuation
How does the ionosphere density change during the course of 24 hours?
Day = higher density Night = lower density
What radio waves does the D layer have no effect on?
HF and above
What are the two layers in the F layer?
F1 and F2
What frequencies pass through the F layer?
UHF and above
Beyond the ionosphere how does attenuation vary with frequency?
Higher frequency = less attentuation
What layer of the ionosphere do HF refract off?
The F layer
What happens to the D layer at night?
It disappears
What happens to the E layer at night?
Moves higher up
What happens to the F layer at night?
They merge into one
What happens to both the E and F laters at night?
Become thinner and less dense
What happens to the amount of refraction at night?
Refraction reduces due to the lower density of the layers
How are radio waves frequencies changed at night?
Lower the frequency
During the day what waves does VLF produce?
Ground and sky waves
During the night what waves does VLF produce?
Ground waves
What is the critical angle sky wave?
The min angle at which the radio wave will refract and return to earth
What is the skip distance?
Distance between the transmitter and the point where the first sky wave arrives
What is the dead space area?
Area between the limit of the ground waves and the first sky wave
How is the dead space area reduced?
Reduce frequency
How is the critical angle reduced?
Lower frequency
What causes super refraction?
A temperature inversion and/or rapid decrease in humidity with height
What are is the effect of super refraction?
Unexpected VHF ranges
